Against

Upon launch in 2011 the Sigma SD1 was an oddity: its 46-megapixel sensor mainstay demanded, or so the company thought, a £5000 price tag. Ouch.

Fast-forward to the beginning of 2012 and what is essentially the very same camera, albeit rebranded as the SD1 Merrill, is available for a fraction of that price – though at £1850 it’s still the most expensive APS-C DSLR on the market by quite a margin.

So what makes the Sigma SD1 special and is it worth the cash?

Colour information

The SD1 is all about its Foveon X3 sensor. Its technology is very different to conventional DSLR sensors, which, at least in theory, means it offers a number of imaging benefits.

If a standard DSLR sensor were dissected it would reveal a single layer of pixel sensors, covered by a colour filter array. This filter arranges red, green and blue in a "mosaic" pattern to deliver colour information that the camera can decipher. But the pattern means 50 per cent green and 25 per cent of both red and blue can't deliver full-colour information, so the camera has to interpolate the results – a bit like an educated "guess" – to fill in the gaps.

With the Sigma’s X3 sensor, however, there are three layers – one for each of the red, green and blue colours. This means no colour information is lost and no colour filter array is required either.

So the SD1’s first major benefit is that it can deliver cracking colour rendition, particularly when dealing with red subjects. Great though this may be, in practice this won’t always be the visible case: the camera’s auto white balance system handles poorly and will "dial out" colour, producing washed-out, colour-cast shots in several outdoor conditions. Keep the camera under controlled lighting, or set the white balance manually, however, and the raw files are really rather sumptuous indeed.

How many megapixels?

Although the SD1 does have 46-megapixels, they’re divided across the three layers of the X3 sensor. So, for the purposes of output resolution, it delivers a 14.7MP image at 4704x3136 pixels. Those looking for huge output resolution can find greater resolutions and larger sensors in a variety of competitor cameras. The Sigma’s resolution may not be as huge as first meets the eye, but it does have another trick up its sleeve for excellent sharpness.

Once again, let’s compare a standard DSLR sensor to the Sigma’s X3 technology: The aforementioned colour filter array requires interpolation that can result in a variety of problems such as moiré and colour artifacts. This may be seen as that "motion fuzz" that you might see on pinstripe-suit-jacket-wearing TV newsreaders, for example. To counteract this an anti-aliasing filter blurs the incoming light slightly – but this is at the expense of sharpness.

Thanks to the Foveon X3 design in the SD1 there’s no need for a colour filter array and, therefore, no anti-aliasing filter either. This will offer an immediate benefit to sharpness for any user, though probably more notably for high-end studio or landscape photographers seeking that extra level of crispness. It’s here that the SD1 does shine: the shots we got from this test were bitingly sharp when shooting at ISO 100.

Does image quality deliver?

The SD1 isn’t quite as rosy all around as it may sound, however. Despite the obvious benefits to high-spec users, there are imaging issues that will be problematic for more casual users, those wanting to shoot in low light or, on account of the slow - for this price point - autofocus system, action photographers.

Shots at ISO 100 are great. Full of grain-like texture that’s akin to film, there’s stacks of detail on offer. But the moment the ISO increases it takes a significant dive. ISO 200 is usable, but image noise is notable from ISO 400 and considerable and even "banded" in appearance from ISO 800. Notch up to ISO 1600 and results are poor, further amplified at ISO 3200 where shots are more or less unusable. The ISO 3200 examples we shot destroyed any detail in dark areas and gradients crumble away owing to the level of noise. Not good.

It’s this poor mid-high ISO performance that will rule out a huge portion of buyers. Yes, ISO 100 is great if you can control light or make longer exposures, but those that want to shoot above ISO 200 would be better off choosing a different system altogether. Considering the clever way the Foveon X3 technology works, it’s a surprise that high ISO shots are quite as bad as they are.

The exposure system, too, responds very differently when compared to other DSLR systems. It’s not uncommon for overexposure and the four-option exposure system takes some getting used to before you feel like you’re in control. This, plus the poor auto white balance system don’t add up to making a good consumer camera.

In use

But it’s not only high ISO image quality that’s a let down. The SD1 doesn’t offer a live view system; rendering a file to the CF card takes too long; the viewfinder is limited to a 98 per cent field of view - it really ought to be 100 per cent at this price point, regardless of sensor technology complications - and the 11-point AF system just isn’t speedy enough.

Current Sigma users will find the SD1 different to previous SD DSLR models as the sensor is slightly larger. The 1.5x magnification is more similar to the Nikon/Sony/Pentax APS-C size sensors, unlike the earlier SD15’s 1.7x magnification.

One rather cool quirk is the addition of a removable infrared-meets-dust-protector filter mounted in front of the sensor. This circular-fit filter can be removed to enable infrared shooting – something that would cost hundreds of pounds (and be permanent) in other DSLR systems. It’s a useful feature if IR shooting is your thing.

Verdict

The SD1 is tricky to judge. For the casual user the camera is unlikely to be suitable: it lacks provisions such as live view; autotofocus is slow; and high ISO image quality is very poor. It’s far from an all-rounder.

But put it in a controlled environment with a decent lens attached, sensitivity set to ISO 100 and the SD1 can be quite spectacular. Rich-colour, biting sharpness that outshines other DSLR cameras and the absence of moiré will have some studio photographers champing at the bit.

Remove the IR filter and stylised infrared photography is also possible – great for quirky landscapes. So for those groups the SD1 may well be a 10/10-scoring camera that represents great quality and value.

Speaking of value, the adjustment of price - the Merrill dropped the original SD1’s price by some £3200 - does make the SD1 all the more accessible. Yet it’s still expensive. For the more casual user there’s little here to admire - it’s strictly one for pros in the know.